In a typical pot, around 40 steel bars are embedded in the carbon cathode and are used as current collector bars to carry current from the cell. These collector bars are then individually fastened by bolts to copper tabs fixed to flexible aluminium straps which are welded to the aluminium ring bus-bar system. Alternatively, an aluminium to steel transition joint is employed for the connection of the collector bar to the aluminium strap, this transition joint being welded on installation and cut at the time of pot removal.
For the bolted connections, contact pressure is critical to an acceptable joint.
A low resistance joint, typically 6 to 8 micro ohms, at these collector bar to strap connections (bar/strap connections) is very important to the efficiency of the process. High resistance joints limit the current able to be efficiently passed through the potline, cause higher than normal pot voltage and will cause unstable pot operation.
Collector bars are made from steel in order to withstand the high temperatures encountered during cell operation. Typically, the bar/strap connection effectively operates at a temperature of about 300.degree. C. Steel has relatively poor electrical properties and this makes it difficult to achieve a good connection between the collector bar and the strap.